Method of strengthening na2o-al2o3-sio2 glass-ceramics with leaded glazes and product



nited States Patent 3,473,937 I /EETHUD OF STRENGTHENING Na O-A1 0 -Si0GLASS-CERAMICS WITH LEADED GLAZES AND PRODUCE Megumi Tashiro, Kyoto,Masamichi Wada, Otsn, Toshio "ice glaze which combines with the baseceramics. By this patent method, a mechanically strong composite bodywas sometimes obtained, but not always. Therefore, the method does notinclude necessary conditions to prepare a mechanically strong compositebody by applying a glaze on Yamimaka, Kym), 31391 Kellichi Tani, 01511,E 5 the glass-ceramics. This invention, however, is concerned giggig iggffgg g to uwens'mmmsa with a method for strengthening the baseglass-ceramics N0 fi Jan 21 1966 Ser No 522 034 by applying a glaze, andincludes the necessary conditions maims applicatioil Japan, Jan P 19%5,for the strengthening of the glass-ceramic. In another asfig/a gg F 1219 5 A ry 050 pect, the invention is concerned with a new glazedglassint. Cl. c0410 35/18; C03c 5/02, 3/04 mi pr u US. Cl. 106-39 2Claims TABLE 1 Example 1 2 3 ABSTRACT OF TEE DISCLOSURE p PartsbyWeight: A glass-ceramic article of the SiO -Al O -Na O-ZrO 10 S10! g2 g8g2 ZnO and/ or MgO system having a vitreous glaze thereon, 17 20 16which glaze has a coeflicient of thermal expansion of 20 5 2 g to 60% ofthe glass-ceramic and the glaze is of the SiO 2 B O -PbOalkali metaloxide System. A method for mak- B O 6 ng e glass-ceramic article is alsodisclosed. 20 fi gg @755 Glass ceramicbase 1,950 1,130 1,675 Glazedmaterial 3,750 2,375 1, 665 Expansion coetfieient -l0l' (30386 C.)/ 0.:This invention 1s concerned with a method for strengthglass ce rar ui sg1; & i e t enlpg glass'ceramlcs y applylng on the glassceramlc:Difierii fehn the expansion coeificient between Which is made up largelyOf ZIOZ, SiO A1203, N320, Z110, 29 the glaze and the glass ceramicbase(percent). 42 45 41 and M 0, a laze which is com osed mainl of SiO Q B03 j i alkali metal oxi 5 (Li 0 O K Table 1 shows the composition of theglass-ceramic i g a coefiicient of thermal ex b 2 r base. ThlS tableclearly shows that the presence of ZnO an, C th t 2 1 i or MgO isextremely important to the strengthening effect Z; a 1S 0 0 ess an a o30 of the glazing. It is shown in Examples 1 and 2, which f g gz ig s'found that a "om osite Ceramic contain ZnO and MgO in the glass-ceramicrespectively, bsymade by applyinw a proper g g proper glass that themechanical strength becamdebmuclzi greater afte;

i g X ceramic base is mechanically stronger than the glassg g ffi g g? grg s g 23%??? i' gfi i ceramic base itself, if the glass-ceramic baseand the glaze h j 1 b l are selected from th followin ran e of chemicalcombase the Increase m the mec Strfi-ngt y g aZ-mg 05mm? the ohsyczramicconiains b Weight was not observed, although the difference In theexpansion g parts f 38 Parts of A1 0 22 z of coefficient between theglass ceramic base and the glaze was of a similar order to those ofExamples 1 and 2. Na 0 as essential ma or com onents. In addition to themaior components 0.5 parts of ZrO and 1-10 parts of Example 3 belongs tothe method referred to Wnhm h ZnO or MgO or a mixture thereof (based on100 parts of 40 3 :3: fggi gf g zgg g gggi z i i i gfiz2 1 ggi gfi gii ggi ggg gg 322 23223: 32 5: necessarily include essential conditions forstrengthening g c g c from by thermal in situ crystallization. At least95% of ai cerartmf: d the total weight consists of the essentialcomponents. The 6 presgl mven Ion 1s conceme W a process O1 2128consist; essentially of by Weivht 4040 parts Sio which condltionsnecessary to strengthen the glass-ceramic 5 parts of B203 10 30partS iand Pa base by glazing are fulfilled. Further practical examples ofalkali metal oxides (Li O, Na O, K 0), and these comare shown bdow'TABLE 2 ponents constitute at least 80% of the total weight of theglaze. Also, the glaze should have an expansion coeflicient Bending strength Ex ansir ooegierwhich is 20-60% less than that of the baseglass-ceramic (kg/cm") en on which the glaze is applied. Glass G G1 d G1G Although the Patent Showa 39/ 19,978 describes a methgs? Glaze g ffgi, i; gg ed to prepare a composite body of a glass-ceramic and a glaze,the method is concerned, as shown in the claims 2 3:21;; E21; 3'; of thepatent specification, with a manufacturing method 3 A 1,920 3,750 i ss68.7 of mixed ceramics mainly for ceramic ware for table or g *2 3% g113:3 23- similar uses; the material is characterized in that a semis A1,000 3,140 109.0 68.7 crystalline glass ceramic base and anintermediate layer g g 2322 E3 31%; (which contains alkali metal oxide,such as Li O, Na O, a o 1:920 3:355 118.8 90.4 or K 0 or theircombination, 16% by weight or less and 3 A 2,115 110430 tend to combinewith the crystals) form an amorphous E ti ated,

TABLE 3 Glass- 53 sioz A1203 Naio ZrOz ZnO MgO 'liOz BaO K10 41 35 18 4s s0 30 20 5 10 50 33 17 1 2 3 50 30 20 2 0 3 50 34 1s 1 2 2 3 50 34 1s1 2 3 52 32 1s 2 6 3 51 32 17 1 2 3 TABLE 4 Glaze SiOz B203 PbO A1203NazO K20 MgO CaO 50 10 24 5 7 2 2 50 1O 21 5 7 5 2 50 10 1S 5 1O 5 2 4410 24 5 7 2 2 6 In making the glasses for the glass-ceramic and for theglazes herein, it will be understood that standard batch materials canbe used, such as silica sand (Slo alumina (A1 soda ash (for Na O),zircon (for ZrO SiO TiO potash (for K 0), ZnO, BaCO (for BaO), Li CO(for Li O), periclase (for MgO), aluminum or sodium phosphate (for P 0boric acid, borax or anhydrous B O CaCO (for CaO), and red lead (forPbO).

The glass batch materials were mixed to result in the chemicalcomposition shown in Table 3 and in Table 1. The mixture of each batchwas-heated at 1550 C. for 8 hours in an electric furnace; then the meltwas shaped in the form of a rod approximately 5 mm. in diameter. Thisglass sample was heated at 800 C. for two hours, then raised to 1100 C.at a rate of 5 C./min. Then by heating further at 1100 C. for two hours,it was converted into a glass-ceramic. Then it was cooled in thefurnace.

The glaze slip was prepared as follows with the chemical compositionsshown in Table 4. The glass mixture was heated at l300-1400 C. for 4-5hours in a gas furnace and the molten material was immersed in water tomake frit. This was placed in a pot-mill together with an appropriateamount of water and a peptizing agent and ground to pass through 200mesh. This glaze slip thus prepared was painted on the ceramic base inthe usual manner and dried. Then it was heated at 1100 C. for two hoursto complete the glazing. The glaze layer was adjusted to become 0.1-0.2mm. thick.

The bending strength shown in Tables 1 and 2 for the glass-ceramic andthe glazed glass-ceramic was measured as follows: a rod specimen 50 mm.long and 5 mm. in diameter was tested with a strength tester which has aspan of 40 mm. and at the middle of the span a load is applied. Theresults presented in Tables 1 and 2 show that the bending strength ofthe glass-ceramic has been increased considerably by the glazing, exceptin the case of Example 3 of Table 1.

Example 14 Glass rods were made as described for the other examples butthe composition of the glass was as follows.

The rods were heat treated by holding at 750 C. for two hours, thenraising the temperature at a rate of 5 C./min. to 1000 C. and holding atthat temperature for two hours. The thermally crystallized rods werethen allowed to cool in the furnace to room temperature. They had abending strength or modulus of rupture (average of a number ofsamplings) of 1210 kg./cm. and a linear coefiicient of thermal expansion(30380 C.) of 119X l0 C.

As in the other examples, a glaze slip was applied, but glaze D in Table4 was used. After drying the composite was heated at a rate of 5 C./min.to 1000 C. where it was held for two hours, then allowed to cool in thefurnace to room temperature. The modulus of rupture of the glazedglass-ceramic was 3400 kg./cm. The thermal expansion of glazecomposition D is 73 10 QT. (30-380 C.).

The reasons that the ranges of chemical composition of the necessarycomponents (SiO A1 0 Na O, ZrO ZnO and MgO) are limited as describedabove is as follows: as to the ZrO at less than 0.5 part difficultieswere encountered in efforts to obtain a finely crystallized glassceramicand at 5 parts or more the liquidus temperature of the glass becomesvery high and the formation of glass becomes diflicult. Therefore, ZrOshould be in a range of 0.5-5 parts. As to the SiO at 45 parts or lessthe chemical resistance of the glass-ceramic is poor, and at 57 parts ormore the crystallization of the glass by reheating was difiicult toaccomplish. Therefore, the SiO content should be in a range of 45-57parts. At 29 parts of A1 0 or less, finely crystallized glass-ceramicwas not obtained easily, and at 38 parts or more the liquidustemperature of the glass became very high. Therefore, the A1 0 should bein a range of 29-38 parts. At 13 parts of Na O or less thecrystallization of the glass by the reheating was difiicult, and at 22parts or more finely crystallized glass-ceramic was not obtained easily.Therefore, the Na O should be in a range of 13-22 parts. When the ZnOand/or MgO content was less than 1 part or more than 10 parts, a finelycrystalline glass-ceramic was not obtained easily; also with less than1% the glaze will not effectively strengthen the glass-ceramic.Therefore, the ZnO and/or MgO content should be in a range of l-lOparts. When the total weight of SiO A1 0 Na O, ZrO and ZnO and/or MgO isbelow 95%, deformation due to softening is considerable in therecrystallization process. Therefore, the total of SiO A1 0 Na O, ZrOZnO and/ or MgO should be more than 95% The reasons that the chemicalcomposition of the glaze in this invention is limited to the rangesmentioned above are to increase the strength of the glass-ceramic bycreating a compressive stress in the glaze layer, and also to bring thesoftening or melting point of the glaze at least below 1150 C. so thatthe glass-ceramic base does not deform in the glazing process, and alsoto give enough chemical resistance to the glaze layer for practical use.At 40 parts or less of SiO;, or at 30 parts or more of B 0 or at 30parts or more of PhD, the chemical resistance of the glaze was poor. Itwas diflicult to obtain a glaze having a lower glazing or curingtemperature than the softening temperature of the glass-ceramic base at70 parts or more of SiO 5 parts or less in B 0 and 10 parts or less inPbO. Therefore, those concentration ranges were determined for SiO 40-70parts, for B 0 5-30 parts and for PbO 10-30 parts. At 2 parts or less inalkali metal oxides (total of H 0, Na O and K 0) the glazing temperatureexceeds the softening temperature of the ceramic base, and at 20 partsor more the expansion coefficient of the glaze was not proper to keepthe difference of 20-60% from that of the ceramic base. Therefore, theconcentration range of the total alkali metal Oxides (Li O, and Na O andK 0) should be within 2-20 parts. In the case where the sum of SiO B 0PbO and alkali metal oxides is less then the expansion coeflicient, theglazing temperature and the chemical composition do not fulfill therequirements described above. Therefore, the total of SiO B 0 PbO andalkali metal oxides must be at least 80% of the total weight.

According to the method described in the present invention, a glazedglass-ceramic having a large strength can be produced. Such products aresuitable for use as tableware as well as industrial materials which needextra strength.

What is claimed is:

1. A composite article comprising (1) a thermally crystallized glasshaving a composition consisting essentially of, in parts by weight: 1

45-57 SiO 13-22 Na O and, based on 100 parts SiO plus A1 plus Na O,

0.5- ZrO and 1-10 of a member selected from the group consisting of ZnO,MgO and a mixture thereof where said SiO +Al O +Na O+ZrO+ZnO+MgO is atleast 95 weight percent of said composition, and (2) a glaze on thesurface of said crystallized glass under compressive stress and having acomposition consisting essentially of, in parts by weight, 40-70 SiO5-30 B 0 -30 PbO, and 2-20 total alkali metal oxides selected from Li O,Na O and K 0, the coeificient of thermal expansion of said glass being-60% less than that of said thermally crystallized glass.

2. A method of making a strengthened glass-ceramic article whichcomprises providing a glass-ceramic article resulting from thermalcrystallization of a glass article of a composition consistingessentially of, in parts by weight,

-57 SiO 13-22 Na O and, based on 100 parts SiO plus A1 0 plus Na O,

0.5-5 ZrO and l-lO of a member selected from the group consisting ofZnO, MgO and a mixture thereof Vhfiffi Said iS at least 95 weightpercent of said composition, and applying thereto a vitreous glazehaving a coefficient of thermal expansion 20 to of that Of theglass-ceramic and having a composition consisting essentially of, inparts by weight, 40-70 SiO 5-30 B 0 lO-3O PhD, and 2-30 total alkalimetal oxides selected from Li O, Na O and K 0.

References Cited UNlTED STATES PATENTS 2,467,114 4/1949 Deyrup 106493,146,114 8/1964 Kivlighn 10639 3,252,811 5/1966 Beall 106-39 3,272,6109/1966 Eppler et al. 106-39 X 3,282,712 11/1966 Tashiro 61: a1. 106-393,384,508 5/1968 Bopp et al. 106 54 X OTHER REFERENCES Kingery, W. D.,Introduction To Ceramics, New York, John Wiley & Sons, 1960, pp.624-625.

HELEN M. MCCARTHY, Primary Examiner W. R. SATTERFIELD, AssistantExaminer US. Cl. X.R.

